Database
[{"id":"1","ip":["82.102.20.247","82.102.20.243"]},{"id":"2","ip":["82.102.20.247","82.102.20.248"]}]
Query
db.collection.aggregate([{$project:{_id:0,id:1,ip:1}},{$unwind:"$ip"},{$group:{_id:"$ip",ids:{$push:"$id"},count:{$sum:1}}},{$match:{count:{$gte:2}}},{$group:{_id:null,ips:{$push:{k:"$_id",v:"$ids"}}}},{$replaceRoot:{newRoot:{$arrayToObject:"$ips"}}}])